Semiconductor integrated circuit device including dummy patterns located to reduce dishing

ABSTRACT

A large area dummy pattern DL is formed in a layer underneath a target T 2  region formed in a scribe region SR of a wafer. A small area dummy pattern in a lower layer and a small area dummy pattern Ds 2  in an upper layer are disposed in a region where the inter-pattern space of a pattern (active regions L 1 , L 2 , L 3 , gate electrode  17 ), which functions as an element of a product region PR and scribe region SR, is wide. The small area dummy pattern Ds 2  in the upper layer is offset by ½ pitch relative to the small area dummy pattern Ds in the lower layer.

BACKGROUND OF THE INVENTION

This invention relates to a semiconductor integrated circuit device andto a process for manufacturing the same and, in particular, theinvention relates to a process which can effectively be applied to asemiconductor integrated circuit device comprising a step for flatteninga surface using CMP (Chemical Mechanical Polishing).

In semiconductor integrated circuit devices, such as a DRAM (DynamicRandom Access Memory), demand has been increasing in recent years forfiner detail and a higher degree of integration. Due to the demand forgreater detail in semiconductor integrated circuit devices, laminatedstructures in multilayer interconnections are unavoidable, but if amultilayer structure is used, imperfections are formed on the surface ofthe upper layer reflecting the imperfections in the substrate. Ifphotolithography is performed when imperfections are present on thesurface, sufficient tolerance of focal depth cannot be obtained in theexposure step, and this leads to poor resolution. Therefore, the surfaceis flattened using CMP in order to improve the photolithography ofcomponents formed on the surface.

The CMP technique is used also to form isolation regions. In the LOCOS(Local Oxidation of Silicon) technique, which was frequently used in thepast, it is difficult to achieve more than a certain amount of detaildue to the presence of a bird's beak. Thus, a shallow groove is formedon a main surface of the semiconductor substrate; this groove is filledwith a silicon oxide film; and the silicon oxide in the regions outsidethe groove are removed by CMP to form a shallow groove isolation. With ashallow groove isolation, the periphery of the isolation region issharply defined, so the periphery can also be used effectively as anelement part, so that it is easier to achieve finer detail.

However, when the CMP technique is used for polishing, it is impossibleto completely remove surface imperfections. When there are imperfectionson the polishing surface, a history of imperfections remains on thepolishing surface to some extent. Further, if parts which are easilypolished and parts which are difficult to polish are both present on thepolishing surface, dishing (polishing depressions) tends to occur in thepart which is easy to polish. Due to the nature of polishing in the CMPmethod, this history of imperfections or dishing is particularlysignificant when the imperfections or parts which are easy to polishhave a large area. Specifically, in polishing by the CMP method,although small imperfections can be flattened relatively well,undulations (global undulations) remain over a large area when a largepattern (usually of the order of several μm or more) is repeated, forexample, and so it is difficult to flatten the surface completely.

However, a method has been proposed where a dummy pattern is disposed inregions where there are large patterns or where there is a wide patterninterval. In this method, the pattern interval is decreased due to thedummy pattern, so that the aforesaid wide area (global) dishing orundulations are suppressed. For example, in Japanese Unexamined PatentPublication No. Hei 10-335333 (1998) (Koho) (U.S. Ser. No. 09/050,416,Mar. 31, 1998), a technique is disclosed wherein a dummy pattern isdisposed in a region with a wide pattern interval to improve theflatness of the surface of an insulating film which fills the pattern.

SUMMARY OF THE INVENTION

By disposing a dummy pattern in a region where there is a large distancebetween patterns, so as to decrease the pattern interval, it is possibleto deal with the problem of dishing (depressions) or undulations over awide area. In dishing, the larger the area is the lower the position ofthe depression in the central part is; and, therefore, by disposing thedummy pattern so as to decrease the area over which dishing occurs, thedepth of the depression can be relatively decreased.

Nevertheless, no matter how small the pattern interval is made, dishingcannot be completely eliminated. When the problem surface to beflattened is a single layer, the depression amount is largely improvedcompared with the dishing which occurs in large area parts, but when thelayer to be flattened is a laminate of plural layers, dishing components(depressions) are superimposed due to the positioning of the pattern,and a large amount of dishing occurs in the upper layer. In such a case,there is a decreased tolerance in the focal depth when photolithographyis performed on the upper layer in a photolithography step, theoveretching amount in an etching step increases, and the yielddecreases.

In regions, such as scribe regions, in which elements which becomeproducts are not normally formed, a target is formed for an exposuredevice (such as a stepper or the like) which is used inphotolithography. A dummy pattern cannot be disposed on the periphery ofthis target as it is necessary to recognize the pattern. The area of thetarget is normally of the order of several μm or more. Therefore, if adummy pattern is not disposed in this large (large area) pattern region,dishing occurs as described above. In the prior art, as this large areapattern was formed in a scribe region and not in a product region, thiswas not considered to be a problem. However, the dishing in the scriberegion also affects the product region, and since the tolerance of focaldepth in the exposure step is becoming more critical due to the trendtowards higher detail, the decreased flatness of the product region (inparticular the periphery) is a matter of concern.

It is therefore an object of this invention to suppress dishing on asurface to be flattened comprising a laminate of plural layers.

It is another object of this invention to improve surface flattening ina pattern region having a large area for optical position detection suchas a target.

It is still another object of this invention to improve a surface to beflattened comprising plural layers, or the flattening of a pattern oflarge area such as a target, thereby improving the patterning margin ina photolithography step and etching step.

The aforesaid and other objects of this invention and novel featuresthereof will become apparent from the following description and appendeddrawings.

Of the inventive features disclosed in the present application, the mosttypical can simply be summarized as follows.

A semiconductor integrated circuit device according to this inventioncomprises a semiconductor substrate having a semiconductor elementformed on a main surface, a first pattern comprising a dummy patternformed on the main surface or on one of the layers on the main surface,and a second pattern formed on an upper layer of the first pattern andcomprising a pattern which serves as a target for optical patternrecognition, the pattern which serves as a target for optical patternrecognition being enclosed within the flat shape of the dummy pattern.According to this semiconductor integrated circuit device, the dummypattern is disposed underneath the pattern used for optical patternrecognition, so that a decrease of the overall flatness in this patternregion is suppressed.

The first pattern may contain another dummy pattern having a smallerarea than the dummy pattern. The dummy pattern and another dummy patternmay also be formed in a scribe region. Further, other dummy patterns maybe formed in a product region and a scribe region.

The dummy pattern is formed with an area equal to or greater, than apattern prohibition region on the periphery of the pattern used foroptical pattern recognition. Therefore, a decrease in the recognitionrate of optical pattern recognition of this pattern is prevented.

The first pattern has patterning dimensions of the same order as thedesign rule of the semiconductor elements and contains another dummypattern having a smaller area than the dummy pattern, but the otherdummy pattern is not disposed in the pattern prohibition region. In thisway, by disposing a small area dummy pattern, except in the vicinity ofthe pattern used for optical pattern recognition, the flatness of theseregions is improved, and by prohibiting provision of the small areadummy pattern in the vicinity of this pattern, a decrease in therecognition rate of the pattern used for optical pattern recognition isprevented.

The dummy pattern is formed in the scribe region of the semiconductorwafer, and the other dummy pattern is formed in the product region andscribe region of the semiconductor wafer. Hence, the flatness of thescribe region, as well as that of the product region, is improved, andthe flatness in the vicinity of the boundary of the product region andscribe region is improved. This contributes to improvement of theproduct yield.

The semiconductor integrated circuit device according to this inventioncomprises a semiconductor substrate having a semiconductor elementformed on its main surface, a first pattern formed on the main surfaceor on one of the layers on the main surface, and a second pattern formedon an upper layer of the first pattern. The first pattern comprises afirst dummy pattern, the second pattern comprises a second dummy patternhaving a pattern pitch and pattern width of identical design dimensionsto those of the first dummy pattern, and the second dummy pattern isformed over a space of the first dummy pattern in its flat position. Oneof the side edges of the second dummy pattern is formed so as to overlapwith the first dummy pattern in its flat surface position, or the firstdummy pattern and second dummy pattern are offset by a distance of ½pitch in its flat surface position. In such a semiconductor integratedcircuit device, dishing does occur in the pattern interval between firstsmall area dummy patterns, but the second small area dummy pattern isformed in the upper layer of the part where this dishing occurs, so thatoverlapping with the dishing formed between the second small areapatterns is prevented. As a result, overlapping of dishing between upperand lower layers is suppressed, and flatness is improved.

In this semiconductor integrated circuit device, the first pattern mayfurther comprise another dummy pattern having a larger area than that ofthe first dummy pattern, the second pattern may further comprise apattern used for optical pattern recognition, and the pattern used foroptical pattern recognition may be enclosed within the flat shape of theother dummy pattern. The other dummy pattern is formed with an areaequal to or greater than the area of the pattern prohibition region onthe periphery of the pattern used for optical pattern recognition, andthe first dummy pattern is not disposed in the pattern prohibitionregion. The other dummy pattern may also be formed in the scribe regionof the semiconductor wafer, and the first and second dummy patterns mayalso be formed in the product region and scribe region of thesemiconductor wafer.

In all of the aforesaid semiconductor integrated circuit devices, thefirst pattern may be an active region pattern formed on the mainsurface, and the second pattern may be a pattern formed in the samelayer as that of the gate electrode forming the semiconductor elements.

The method of manufacturing the semiconductor integrated circuit deviceof this invention comprises (a) a step of forming a first patterncomprising a dummy pattern on the main surface or on any componentsurface on the main surface of a semiconductor substrate, (b) a step ofdepositing an insulating film on the main surface on which the firstpattern is formed or on a component patterned on the first pattern, andflattening the surface by polishing the insulating film, and (c) a stepof forming a second pattern comprising a pattern used for opticalpattern recognition on the upper layer of the flattened surface. Thepattern used for optical pattern recognition is enclosed within the flatshape of the dummy pattern.

In this manufacturing method, a step may further be provided fordetecting the pattern used for optical pattern recognition to performalignment of the semiconductor substrate.

Alternatively, the method of manufacturing the semiconductor integratedcircuit device of this invention further comprises (a) a step of forminga first pattern comprising a dummy pattern on the main surface or on anycomponent surface on the main surface of the semiconductor substrate,(b) a step of forming a second pattern comprising a pattern used foroptical pattern recognition on the upper layer of the first pattern, and(c) a step of detecting the pattern used for optical pattern recognitionto perform alignment of the semiconductor substrate. The pattern usedfor optical pattern recognition is enclosed within the flat shape of thedummy pattern.

In either of the manufacturing methods described above, the dummypattern may be formed with an area equal to or greater than the patternprohibition region on the periphery of the pattern used for opticalpattern recognition.

The first pattern further comprises a first dummy pattern, and thesecond pattern further comprises a second dummy pattern having a patternpitch and pattern width identical to the design dimensions of the firstdummy pattern, the second dummy pattern being formed over a space of thefirst dummy pattern in its flat surface position.

One of the side edges of the second dummy pattern is formed so as tooverlap with the first dummy pattern, or the first dummy pattern andsecond dummy pattern are offset at a distance of ½ pitch in its flatsurface position.

The dummy patterns may be formed in the scribe region of thesemiconductor wafer, and the first and second dummy patterns may beformed in the product region and scribe region of the semiconductorwafer.

The component to which the first pattern is transferred is thesemiconductor substrate, and the component to which the second patternis transferred is the gate electrode.

The aforesaid semiconductor integrated circuit device can bemanufactured by these semiconductor integrated circuit devicemanufacturing methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a silicon wafer used for manufacturing asemiconductor integrated circuit device according to one embodiment ofthis invention.

FIG. 2 is a plan view showing an enlargement of a chip part of a waferaccording to this embodiment.

FIG. 3 is a plan view showing an end region of the chip comprising ascribe line.

FIG. 4 is a plan view showing an enlargement of a product region of thechip.

FIG. 5(a) and FIG. 5(b) are sectional views showing an example of amethod of manufacturing the semiconductor integrated circuit deviceaccording to the embodiment as a sequence of processes.

FIG. 6(a) and FIG. 6(b) are sectional views showing an example of amethod of manufacturing the semiconductor integrated circuit deviceaccording to the embodiment as a sequence of processes.

FIG. 7(a) and FIG. 7(b) are sectional views showing an example of amethod of manufacturing the semiconductor integrated circuit deviceaccording to the embodiment as a sequence of processes.

FIG. 8(a) and FIG. 8(b) are sectional views showing an example of amethod of manufacturing the semiconductor integrated circuit deviceaccording to the embodiment as a sequence of processes.

FIG. 9(a) and FIG. 9(b) are sectional views showing an example of amethod of manufacturing the semiconductor integrated circuit deviceaccording to the embodiment as a sequence of processes.

FIG. 10(a) and FIG. 10(b) are sectional views showing an example of amethod of manufacturing the semiconductor integrated circuit deviceaccording to the embodiment as a sequence of processes.

FIG. 11(a) and FIG. 11(b) are sectional views showing an example of amethod of manufacturing the semiconductor integrated circuit deviceaccording to the embodiment as a sequence of processes.

FIG. 12(a) and FIG. 12(b) are sectional views showing an example of amethod of manufacturing the semiconductor integrated circuit deviceaccording to the embodiment as a sequence of processes.

FIG. 13(a) and FIG. 13(b) are sectional views showing an example of amethod of manufacturing the semiconductor integrated circuit deviceaccording to the embodiment as a sequence of processes.

FIG. 14(a) and FIG. 14(b) are sectional views showing an example of amethod of manufacturing the semiconductor integrated circuit deviceaccording to the embodiment as a sequence of processes.

FIG. 15(a) and FIG. 15(b) are sectional views showing an example of amethod of manufacturing the semiconductor integrated circuit deviceaccording to the embodiment as a sequence of processes.

FIG. 16(a) and FIG. 16(b) are sectional views showing an example of amethod of manufacturing the semiconductor integrated circuit deviceaccording to the embodiment as a sequence of processes.

FIG. 17 is a plan view showing an example of a method of manufacturingthe semiconductor integrated circuit device according to the embodimentas part of a sequence of processes.

FIG. 18 is an enlarged plan view of FIG. 17.

FIG. 19(a) and FIG. 19(b) are sectional views showing an example of amethod of manufacturing the semiconductor integrated circuit deviceaccording to the embodiment as a sequence of processes.

FIG. 20(a) and FIG. 20(b) are sectional views showing an example of amethod of manufacturing the semiconductor integrated circuit deviceaccording to the embodiment as a sequence of processes.

FIG. 21(a) and FIG. 21(b) are sectional views showing an example of amethod of manufacturing the semiconductor integrated circuit deviceaccording to the embodiment as a sequence of processes.

FIG. 22(a) and FIG. 22(b) are sectional views showing an example of amethod of manufacturing the semiconductor integrated circuit deviceaccording to the embodiment as a sequence of processes.

FIG. 23(a) and FIG. 23(b) are sectional views showing an example of amethod of manufacturing the semiconductor integrated circuit deviceaccording to the embodiment as a sequence of processes.

FIG. 24 is a plan view showing an example of a method of manufacturingthe semiconductor integrated circuit device according to the embodimentas part of a sequence of processes.

FIG. 25 is an enlarged plan view showing another example of thesemiconductor integrated circuit device according to the embodiment.

FIG. 26 is an enlarged plan view showing another example of thesemiconductor integrated circuit device according to the embodiment.

FIG. 27 is an enlarged plan view showing yet another example of thesemiconductor integrated circuit device according to the embodiment.

FIG. 28 is an enlarged plan view showing yet another example of thesemiconductor integrated circuit device according to the embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

One embodiment of this invention will now be described in detail withreference to the drawings. In all of the drawings which illustrate thisembodiment, the same symbols are used for members having identicalfunctions, and their description will not be repeated.

FIG. 1 is a plan view showing a silicon wafer used for manufacturing asemiconductor integrated circuit device according to one embodiment ofthe invention. A notch ln is made in a single crystal silicon wafer 1 wand serves as a crystal plane index mark of the wafer 1 w. A chip 1 c isformed on the wafer 1 w. The chip 1 c is formed in the effectiveprocessing area of the wafer 1 w, and a chip region 1 g outside theeffective processing area is not used.

FIG. 2 is a plan view showing an enlargement of the chip 1 c of thewafer 1 w. The chip 1 c is scribed and divided by a scribe line SL. Inthe steps described hereafter, each step is performed in the state ofthe wafer 1 w, the chip 1 c being divided in the final step.

In this form of the invention, the typical DRAM chip 1 c is shown as anexample. It may also be another product, for example a logic product,such as a CPU, a memory element, such as an SRAM (Static Random AccessMemory), or a memory which can be erased in one step and be electricallyrewritten (so-called EEPROM: Electrical Erasable Read Only Memory), or asystem LSI where a logic circuit and memory element coexist on the samechip. A memory cell array MA, direct peripheral circuit PCd and indirectperipheral circuit Pci are formed in the chip 1 c. DRAM memory cells areformed in the memory cell array MA. The direct peripheral circuit PCd isformed on the periphery of the memory cells MA. The indirect peripheralcircuit Pci is formed in the center region of the chip 1 c.

FIG. 3 is a plan view showing an edge region of the chip 1 c comprisingthe region of the scribe line SL. FIG. 3 shows the state where anisolation region is formed on a semiconductor substrate 1 (wafer 1 w,chip 1 c). The regions other than a scribe region SR are product regionsPR.

A target pattern T1, large area dummy pattern DL and small area patternDs are formed simultaneously when the isolation region is formed in thescribe region SR. A TEG (Test Equipment Group) element is also formed inthe scribe region SR, but it is not shown in the drawings. The targetpattern T1 is a pattern formed simultaneously in a step when anisolation region pattern is formed, and it is used for alignment in anexposure step when a gate electrode pattern, to be described later, isformed. Specifically, it is used as a target for position detection whenmask alignment of a target electrode pattern is performed. In anexposure device, a mask is aligned with respect to the wafer by, forexample, performing optical pattern recognition of the target, and aphotoresist film is then exposed.

The large area dummy pattern DL and small area dummy pattern Ds arepatterns which are simultaneously formed in the step when the isolationregion pattern is formed. A target pattern T2 is formed simultaneouslywith the target electrode pattern on the large area dummy pattern DL.The target pattern T2 is used for alignment in the exposure step whenthe upper layer pattern, for example, an interconnection pattern orconnecting hole pattern, is formed. Due to the provision of the largearea pattern DL, dishing in the target pattern region is prevented, therecognition rate of the target pattern is improved, and fine patterningcan advantageously be performed. In the prior art, a dummy pattern wasnot provided on the periphery of the prior art target pattern, so thatthe surface flatness of the target pattern periphery was impaired;however, by providing the large area dummy pattern DL underneath thetarget pattern, the flatness is improved and the recognition rate of thetarget pattern is improved. The large area dummy pattern DL is formed tobe larger than the target pattern so as to enclose the target pattern.In other words, the large area dummy pattern DL is present underneaththe target pattern region used for optical pattern recognition, so thatdishing is prevented and the recognition rate of the target pattern isimproved. On the periphery of the target pattern, there is a regionwhere any kind of pattern is prohibited, thereby to prevent interferencewith target pattern recognition. The large area dummy pattern DL has anarea equal to or greater than this pattern prohibition region.Therefore, the large area dummy pattern DL is not recognized as apattern by the exposure device, and the recognition rate of the targetpatterns T1, T2 is not decreased.

The small area dummy pattern Ds is formed in the scribe region SR andthe product region PR. In other words, it is formed over the wholesurface of the wafer W. Thus, the small area dummy pattern Ds isdisposed in a region in which there is a wide interval between patternsfunctioning as elements. Since there is a wide interval between patternsfunctioning as elements, if the small area dummy pattern Ds were notdisposed in this wide pattern interval, dishing would occur in thepattern interval. Since this dishing becomes larger in depth as thepattern interval becomes wider, the flatness is largely impaired. Bydisposing this small area dummy pattern Ds in this wide inter-patternspace, the flatness is improved. As the pattern size and inter-patternspace are formed with dimensions of approximately the same order asthose of the pattern forming the elements, the pattern interval isnarrow, and a small amount of dishing according to the narrow patterninterval occurs. In this situation, the depression amount can be muchimproved and the flatness can be improved compared with the case whenthe dummy pattern is not provided. The pattern size of the small areadummy pattern Ds is of the same order as the element design rule, and asuitable value is selected with regard to the ease of photolithographyand the effect on suppression of dishing. When the element design ruleis of the order of, for example, 0.2 μm, the pattern size of the smallarea dummy pattern Ds may also be set to the order of 0.2 μm. However,if a KrF excimer laser is used as the exposure light source, a techniquemust be used to improve the resolution, such as use of a Levenson mask.If priority is given to the ease of forming the mask, the pattern sizeof the small area dummy pattern Ds may be set to be of the order of 1μm, and the inter-pattern space may be set to be of the order of 0.4 μm.It will of course be understood that other figures can be selected fromthe requirements of the photolithography step. However, if the patternsize and inter-pattern space are too large, dishing in the inter-patternspace becomes more marked, which is undesirable.

The width of the scribe region SR is approximately 100 μm.

In FIG. 3, active regions which form elements are formed apart from theaforesaid small area dummy pattern Ds in the product region PR.According to this embodiment, an active region L1 forming a channelregion of a MISFET (Metal Insulator Semiconductor Field EffectTransistor), an active region L2 for well feed and an active region L3for guard band feed are shown as examples. It will be understood thatother active regions may also be formed. The aforesaid small area dummypattern Ds is formed between the patterns of the active regions L1, L2,L3. The large area dummy pattern DL may also be formed in the productregion PR.

FIG. 4 is a plan view showing an enlargement of a region comprising theactive regions L1, L2 of the product region PR. Plural small area dummypatterns Ds are disposed between the patterns of the active regions L1,L2, as described above. As stated above, the pattern size d1 of thesmall area dummy pattern Ds is approximately 1 μm, and the patterninterval S1 is approximately 0.4 μm.

The small Area dummy pattern Ds is formed by automatically generatingpatterns of the aforesaid size in a lattice (grid) with the patternpitch (1.4 μm in the case of this embodiment). At each lattice point,the small area dummy pattern Ds is not generated in parts where theactive regions L1, L2 are present. Specifically, in a mask designdevice, a graphic computation is performed which expands patterns suchas the active regions L1, L2. This expanded pattern region is a patternprohibition region R1 of the small area dummy pattern Ds. Next, of theaforesaid lattice points, the lattice within the pattern prohibitionregion R1 is excluded from the graphic computation, and the small areadummy pat@ern Ds is generated at the remaining lattice points. Thisgenerated small area dummy pattern Ds is added to the active regions R1,R2 to give mask generation data. The pattern prohibition region R1 forthe small area dummy pattern Ds is formed also on the periphery of thelarge area dummy pattern DL. As a result, the pattern to be expandedalso contains the large area dummy pattern DL. In this way, a maskpattern wherein dummy patterns are disposed is easily generatedautomatically. This can also be done manually or automatically bydisposing a layer (pattern layer) corresponding to the patternprohibition region R1, and then specifying positions where it is notdesired to dispose other small area dummy patterns Ds.

Next, the method of manufacturing the semiconductor integrated circuitdevice of this invention will be described, including the steps forforming the aforesaid active regions and a dummy region (isolationregion) DR.

FIG. 5 to FIG. 23 (excluding FIG. 17, FIG. 18) are sectional viewsshowing the sequence of steps in one example of the method ofmanufacturing the semiconductor integrated circuit device of thisinvention. In these sectional views, figures with numbers to which (a)is appended represent a section as seen on a line A—A in FIG. 3 and FIG.4, and figures with numbers to which (b) is appended represent a sectionthrough a line B—B in FIG. 3. In the (a) figures, the dummy region DRwhere a dummy pattern is formed, circuit region CR and voltage supplyregion SR where a voltage supply pattern is formed, are respectivelyshown. In the (b) figures, a target region TR, small area dummy patternprohibition region IR and dummy region DR are respectively shown.

As shown in FIGS. 5(a) and 5(b), the semiconductor substrate 1 (wafer 1w) is provided, and a thin silicon oxide (SiO) film 2 and siliconnitride (SiN) film 3 are formed thereon. The semiconductor substrate 1is a single crystal silicon wafer wherein, for example, p typeimpurities are introduced, and it has a resistivity of the order ofseveral ohmcm. The silicon oxide film 2 is a sacrifice film foralleviating the stress between the silicon nitride film 3 andsemiconductor substrate 1, and it is formed, for example, by thermaloxidation. The silicon nitride film 3 is used as a mask for forming agroove, as will be described later. The film thickness of the siliconnitride film 3 is several hundred nm, and it is formed for example byCVD (Chemical Vapor Deposition).

Next, as shown in FIGS. 6(a) and 6(b), a photoresist film 4 is formed onthe silicon nitride film 3. The photoresist film 4 is formed to coverthe regions where the active regions L1, L2, L3, the large area dummypattern DL and the small area dummy pattern Ds, which were described inFIG. 3 and FIG. 4, are respectively formed. As stated above, regardingthe size of the small area dummy pattern Ds, the fine patterning whichwould be required with a Levenson mask is not necessary, so that in theregion where the small area dummy pattern Ds is formed, there is noimpairment of machinability due to the decrease of focal point tolerancethat is inherent in super-high resolution techniques, such as theLevenson method. This simplifies the mask design.

Next, as shown in FIGS. 7(a) and 7(b), dry etching is performed in thepresence of the photoresist film 4, and the silicon nitride film 3 andsilicon oxide film 2 are etched to remove them.

After the photoresist film 4 is removed, as shown in FIGS. 8(a) and8(b), dry etching (anisotropic etching) is performed in the presence ofthe silicon nitride film 3, and the semiconductor substrate 1 is etchedto form a groove S. The depth of the groove 5 is several hundred nm. Thepattern of the groove 5 formed in this step is the reverse of thepattern of the active regions L1, etc., shown in the aforesaid FIG. 3and FIG. 4.

In this step, the patterned silicon nitride film 3 is used as a hardmask. By using the thin silicon nitride film 3 as a hard mask, theetching properties are improved, and fine patterning can easily beperformed. Instead of using the silicon nitride film 3 as a hard mask,the semiconductor substrate 1 can be etched in the presence of thephotoresist film 4 to form the groove 5. In this case, the steps aresimplified.

Next, as shown in FIGS. 9(a) and 9(b), a silicon oxide film 6 is formedover the whole surface of the semiconductor substrate 1, including theinterior of the groove 5. The silicon oxide film 6 can be formed by CVDusing, for example, TEOS (tetraethoxysilane) gas and ozone (O₃) as rawmaterial gases. The film thickness of the silicon oxide film 6 is a filmthickness sufficient to fill the groove 5.

Next, as shown in FIGS. 10(a) and 10(b), the silicon oxide film ispolished using CMP. The polishing is performed until the surface of thesilicon nitride film 3 is exposed. In this way, the isolation region 7is formed leaving the silicon oxide film 6 only in the region of thegroove 5.

In this process, in the dummy region DR, the small area dummy pattern Dsis formed, so dishing occurs only slightly between the patterns of thesmall area dummy pattern Ds, and the flatness can be remarkably improvedcompared with the case where the dummy pattern is not present. Further,as the large area dummy pattern DL is formed also in the target regionTR, global dishing is prevented, and the flatness in this region isimproved. In the case of this embodiment, the target region TR is formedin the scribe region SR, and deterioration of the flatness in the targetregion TR may occasionally cause a decrease in the flatness in theproduct region PR, which is adjacent to the target region TR. However,according to this embodiment, the large area pattern DL is formed in thetarget region TR, so there is no such effect on the product region PR.

Next, as shown in FIGS. 11(a) and 11(b), the silicon nitride film 3 andsilicon oxide film 2 are removed to expose the active regions L1, L2,L3, large area dummy pattern DL and small area dummy pattern Ds. Theaforesaid FIG. 3 and FIG. 4 show the stage when this step is completed.To remove the silicon nitride film 3, wet etching with hot phosphoricacid is used, for example. Subsequently, the surfaces of the siliconoxide film 2 and isolation region 7 are etched to a suitable degree byhydrofluoric acid (HF), and the substantially flat surface shown inFIGS. 11(a) and 11(b) is obtained.

Next, as shown in FIGS. 12(a) and 12(b), a photoresist film, not shown,is formed; p type or n type impurities are ion implanted; and a deepwell 8, n type well 9 and p type well 10 are formed. The deep well 8functions to electrically isolate the p type well 10 from thesemiconductor substrate 1.

Next, as shown in FIGS. 13(a) and 13(b), a silicon oxide film 11,polycrystalline silicon film 12 and tungsten silicide (WSi) film 13,which function as a gate electrode, and a silicon nitride film 14, whichfunctions as a gap insulating film, are deposited. The silicon nitridefilm 11 is formed, for example, by thermal oxidation or by thermal CVD,and has a film thickness of several nm. The polycrystalline silicon film12 is formed, for example, by CVD, and n type or p type impurities areintroduced into it. The film thickness is several hundred nm. Thetungsten silicide film 13 is formed by CVD or by sputtering, andlikewise, the film thickness is several hundred nm. The tungstensilicide film 13 decreases the sheet resistance of the gate electrode(gate interconnection) and contributes to improving the response speedof the element. The silicon nitride film 14 is formed, for example, byCVD, and has a film thickness of several hundred nm.

Here, the tungsten silicide film 13 was shown as an example, but othermetal silicide films, such as a titanium silicide (TiSi) film or acobalt silicide (CoSi) film may be used. Also, a laminate comprising thetungsten silicide film 13 and polycrystalline silicon film 12 was shownas an example, but laminates of the polycrystalline silicon film, abarrier film and a metal film, such as tungsten (W), may be used. Inthis case, the resistivity of the gate electrode (gate interconnection)can be further reduced. A metal nitride film, such as tungsten nitride(WN), titanium nitride (TiN) or tantalum nitride (TaN), may be used forthe barrier film. In addition to tungsten, tantalum (Ta) or titanium(Ti) can also be used for the metal film.

Next, as shown in FIGS. 14(a) and 14(b), a photoresist film 15 is formedon the silicon nitride film 14, and dry etching (anisotropic etching) isperformed to pattern the silicon nitride film 14, as shown in FIGS.15(a) and 15(b). In this way, a gap insulating film 16 is formed. Thepatterning of this gap insulating film 16 will be described later. Inthe exposure step for forming the photoresist film 15, the target T1 isused for position detection in mask alignment.

Next, the photoresist film 15 is removed by ashing or the like, and thetungsten silicide film 13, polycrystalline silicon film 12 and siliconoxide film 11 are etched (anisotropically etched) in the presence of thegap insulating film 16 to form a gate electrode 17, as shown in FIGS.16(a) and 16 (b)

At this time, a second small area dummy pattern Ds2 and target T2 areformed simultaneously with the gate electrode 17.

FIG. 17 is a plan view showing the situation at this stage,corresponding to FIG. 3. FIG. 18 is an enlarged plan view correspondingto FIG. 4.

As shown in FIG. 17, the target T2 is formed in addition to the smallarea dummy pattern Ds2 in the scribe region SR. The target T2 is usedfor exposure, for example in a step to form interconnections orconnection holes. The target T2 is formed on the large area dummypattern DL so as to be enclosed by it. The pattern prohibition region R2is also formed on the periphery of the target T2 to prevent a decreasein the recognition rate when the target T2 is used later, and the largearea dummy pattern DL is formed to be larger than the patternprohibition region R2. Hence, no pattern other than the target T2 isformed inside the pattern prohibition region R2, so that the target T2can be accurately recognized. Further, since the target T2 is formed onthe large area dummy pattern DL, the target T2 is not formed on adepressed substrate, but is formed on a flattened substrate. Therefore,in a subsequent exposure step using the target T2, the target T2 can beaccurately recognized, and the mask alignment precision is improved.Further, since the large area dummy pattern DL is formed underneath thetarget T2, the flatness of this region is improved, the flatness of itsperiphery, in particular the product region PR adjacent to the targetT2, is improved, which results in an improvement of the photolithographymargin, and etching is easily performed.

The small area dummy pattern Ds2 is also formed in the scribe region SR.This improves the flatness of this region. However, it is not disposedin the small area dummy pattern prohibition region R1. The small areadummy pattern Ds2 will be described later.

The gate electrode 17 is formed in the product region PR. Plural smallarea dummy patterns Ds2 are disposed between the patterns of the gateelectrode 17. As in the case of FIG. 3, they are not disposed in thesmall area dummy pattern prohibition region R2. The pattern prohibitionregion R1 is formed in the same way as described above.

The small area dummy pattern Ds2 is formed on the inter-pattern spacesof the small area dummy pattern Ds of the lower layer, as shown in FIG.18. Specifically, the pitch of the small area dummy pattern Ds2 and thatof the small area dummy pattern Ds in the layer underneath are offset by½. In other words, the small area dummy pattern Ds2 is offset by Px inthe x direction and by Py in the y direction with respect to the smallarea dummy pattern Ds. Px, Py are, for example, both 0.7 μm. In thisway, by forming the small area dummy pattern Ds2 with an offset of ½pitch, the effect of dishing in the layer underneath is eliminated andthe flatness is improved. In other words, the dishing of the layerunderneath occurs in a space part of the small area dummy pattern Ds,and since the small area dummy pattern Ds2 is formed on top of it, thedishing is not superimposed. Dishing due to the small area dummy patternDs2 occurs in its space part, but as the small area dummy pattern Ds isformed in the layer underneath it, dishing does not occur here. In otherwords, by providing the small area dummy patterns Ds, Ds2 as in thisembodiment, dishing does not occur in the layer above the region wheredishing occurs in the lower layer, and the part where dishing occurs inthe upper layer is formed over the region where dishing does not occurin the lower layer. Hence, the total amount of dishing due to the twolayers is reduced, and the overall flatness can be increased.

The situation wherein the small area dummy pattern Ds2 of the upperlayer is not formed in the pattern prohibition region R1 is identical tothe case of the small area dummy pattern Ds. Further, the small areadummy pattern Ds2 is generated in an identical way to the small areadummy pattern Ds, except that the lattice positions are shifted by ½pitch.

Herein, a case was described where the small area dummy patterns Ds, Ds2were shifted by ½ pitch, but the shift amount may be any value providedthat the side edge of Ds2 is formed to overlap with Ds1. In other words,Ds2 must be formed in a part above the space part of Ds1.

Next, impurities are ion-implanted to form an impurity semiconductorregion 19, as shown in FIGS. 19(a) and 19(b). Low concentrations ofimpurities are introduced into the impurity semiconductor region 19. Theconductivity of the impurity introduced is chosen according to thechannel type of the MISFET that is being formed. Thus, p type impuritiesare implanted in an n type well region to form a p channel MISFET; and,n type impurities are introduced in a p well region to form an n channelMISFET.

Next, as shown in FIGS. 20(a) and 20(b), a silicon nitride film, forexample, is formed over the whole surface of the semiconductor substrate1, and this is subjected to anisotropic etching to form a side wallspacer 20. Subsequently, ion implantation is performed to form animpurity semiconductor region 21. The impurity ions introduced into theimpurity semiconductor region 21 are chosen to give a suitableconductivity depending on the region, as in the case described above.High concentrations of impurities are introduced into the impuritysemiconductor region 21, and a source/drain having an LDD (Lightly DopedDrain) structure is formed together with the impurity semiconductorregion 19.

Next, as shown in FIGS. 21(a) and 21(b), a silicon oxide film 22enclosing the gate electrode pattern is formed, and as shown in FIGS.22(a) and 22(b), the silicon oxide film 22 is polished by CMP to flattenits surface. During this flattening, since the small area dummy patternDs2 is formed in the same layer as the gate electrode pattern, theflatness is improved. In particular, since the small area dummy patternDs2 is offset by ½ pitch with respect to the small area dummy pattern Dsof the lower layer, the dishing of the two layers in the spaces betweenthe patterns is not superimposed. As a result, a decrease of theflatness due to superimposition of dishing is suppressed. Also, in theregion of the target T2, since the large area dummy pattern DL is formedin the layer underneath, global dishing does not occur, and the flatnessis improved also in the scribe region SR. Hence, there is no adverseeffect on the product region PR, and the yield is improved. Moreover,the small area dummy pattern Ds2 is also disposed in the scribe regionSR, so that the flatness is improved in the same way as in the productregion PR.

Herein, a case was described wherein the target T2 was formed in thescribe region SR, but the target T2 may also be formed in the productregion PR. Further, the target pattern was given as an example of apattern required for pattern recognition, but it will be understood thatthe invention may also be applied to any pattern which can be used foroptical pattern recognition. For example, it may be a testing patternused for quality control in mask alignment, a test pattern formonitoring the film thickness, or a position detecting pattern used forlaser repair.

Next, as shown in FIGS. 23(a) and 23(b), a connecting hole 23 is formedin the silicon oxide film 22, and a connecting plug 24 is formed in theconnection hole 23. An interconnection 25 is also formed on the siliconoxide film 22.

The connecting hole 23 is formed by anisotropic etching using aphotoresist film, not shown, as a mask. When this photoresist film isformed, i.e., for the exposure of this step, the aforesaid target T2 maybe used for position detection in mask alignment. In addition topolycrystalline silicon, laminates of titanium nitride films andtungsten films may, for example, be used for the connecting plug. Toform the connecting plug, a connecting hole is opened, an electricallyconducting material is formed to fill it, and the electricallyconducting film in regions other than the connecting hole is removed byCMP.

The interconnection 25 is formed by anisotropic etching using aphotoresist film, not shown, in the same way. When this photoresist filmis formed, i.e. for the exposure of this step, the aforesaid target T2may be used for position detection in mask alignment. Metal materials,such as tungsten and laminates of, for example, titanium nitride andtungsten, may be used for the interconnection 25. The interconnection 25is formed by forming a film of the metal material, and patterning it.

A multilayer interconnection structure can be formed by forminginterconnections in the upper layers, such as the second and thirdlayers, and since this is identical to the case of the aforesaidinterconnection 25, its description will be omitted.

FIG. 24 is a plan view showing the situation when the wafer process iscomplete, and the scribe region SR is at the scribe stage. The wafer 1 wis divided by the scribe line SL to form the chip 1 c. The width of thescribe line SL is a dimension obtained by adding play to the blade width(e.g., 35 μm) As a result, in the chip 1 c, a region of the order ofseveral tens of μm remains as the distance from the edge of the productregion PR to the edge of the chip 1 c. Part of the aforesaid targets T1,T2, and the large area dummy pattern DL, remain in this residual region.In FIG. 24, a target T3 is shown. This is a target pattern formedsimultaneously when the interconnection 25 of the first layer ispatterned. The target T3 is used to form an interconnection or throughhole in the upper layer.

This invention as conceived by the inventors has been described indetail based on one embodiment of the invention, however it will beunderstood that the invention is not limited to this embodiment, variousmodifications being possible within the scope and spirit of the appendedclaims.

For example, in the embodiment, an example was given where the offset ofthe small area dummy patterns Ds, Ds2 was provided in both the xdirection and y direction, but the offset may be provided in only onedirection.

Further, the case was shown where the small area dummy patterns Ds, Ds2were rectangular, but they may also be of another shape, such as oblong.For example, they may be lattice-shaped dummy patterns, as shown in FIG.25 and FIG. 26. Specifically, a lattice-shaped pattern 26 can be formedsimultaneously with the active region L1, as shown in FIG. 25, or alattice-shaped pattern 27 can be simultaneously formed with the gateelectrode 17 with a ½ pitch shift relative to the pattern 26, as shownin FIG. 26. Alternatively, instead of the small area target patterns Ds,Ds2, line-shaped dummy patterns can be formed, as shown in FIG. 27 andFIG. 28. Specifically, a line-shaped dummy pattern 28 can be formedsimultaneously with the active region L1, as shown in FIG. 27, or aline-shaped pattern 29 can be simultaneously formed with the gateelectrode 17 with a ½ pitch shift relative to the pattern 28, as shownin FIG. 28. These dummy patterns 26, 27, 28, 29 are not formed in thepattern prohibition region R1, which is identical to the case of theembodiment. Further, the sizes of the patterns 26, 27, 28, 29 are alsoidentical to those of the embodiment.

Among the inventive features disclosed in this application, the effectsobtained by representative aspects of the invention may simply bedescribed as follows.

(1) Dishing in plural laminated flattened surfaces is suppressed.

(2) Surface flattening in pattern regions of a large area for opticalposition detection, e.g., of targets, is improved.

(3) The flatness of plural laminated surfaces, or the flatness of largearea patterns, such as targets, is improved, and the machining margin ina photolithography step and etching step is improved.

What is claimed is:
 1. A semiconductor integrated circuit devicecomprising a semiconductor substrate having a semiconductor elementformed over a main surface of the semiconductor substrate, a firstpattern formed on said main surface or any layer on said main surface,and a second pattern formed over an upper layer of said first pattern,said first pattern comprises a plurality of first dummy patterns, saidsecond pattern comprises a plurality of second dummy patterns having apattern pitch and pattern width of identical design dimensions as saidfirst dummy patterns, said second dummy patterns are formed overinter-pattern spaces of said first dummy patterns in its flat surfaceposition, and each second dummy pattern is isolated from each of theother second dummy patterns, wherein: said first pattern furthercomprises another dummy pattern having a larger area than that of saidfirst dummy pattern, said second pattern further comprises a patternused for optical recognition, and said pattern used for opticalrecognition is formed so that it is enclosed within the flat shape ofsaid other dummy pattern.
 2. A semiconductor integrated circuit deviceas defined in claim 1, wherein: said other dummy pattern is formed withan area equal to or greater than that of the pattern prohibition regionon the periphery of the pattern used for optical pattern recognition,and said first dummy pattern is not disposed in said pattern prohibitionregion.